The experimental model is designed to resolve fundamental questions concerning the existence of functional subsets among resident pulmonary alveolar macrophages (PAM). The study will take advantage of the strontium-89 (89Sr) monocytopenic mouse model which provides for the analysis of resident PAM surface marker heterogeneity in the absence of contamination by emigrating monocyte-macrophage. Our objective is to establish the existence of PAM subsets among resident PAM populations, in the absence of monocytes, and to evaluate that ability of those subsets to selectively increase their cell numbers in response to inflammatory stimuli. PAM subset heterogeneity and proliferative activity will be compared and contrasted in normal, outbred mice and in genetically defective inbred strains of mice. Flow cytometry will be used to characterize the subset distribution of a variety of monoclonal antibodies (MABs) to epitopes on the surface of mononuclear phagocytes. 125I-MAB binding studies will measure the number of MABs/PAM while propidium iodine staining will be employed to evaluate the cell cycle times of PAM subsets. Upon defining a battery of subset-specific MABs, subsets will be sorted by fluorescence activated cell sorting and the cell cycle times measured for each subset. ICR mice will be challenged in vivo, with either Candida albicans, Corynebacterium par um vaccine, Listeria monocytogenes, endotoxin or interferon and the effects of challenge on PAM subset surface markers and subset proliferation determined. Similar studies will be performed in C57B1/6bgbg, C3H/HeN, C3H/HeJ, PN, SLSLd and W/Wv mouse strains.